The present invention relates to hopper valve modules of the type which are adapted to be removably mountable in the well of a hopper of a hopper dredge vessel. Such modules are disclosed in my U.S. Pat. No. 4,030,435.
During the operation of the hopper dredge vessel, the valve module is substantially inaccessible since it is located at the bottom of the hopper. Thus, when the valve is closed and the hopper is full, the valve module is covered with the dredged material stored in the hopper and, after the hopper has been emptied, the valve module is partially submerged in water.
As is explained in my aforementioned patent, because of the nature of the dredged material, which may often include large pieces of debris such as logs, large rocks and the like, the valve member can become jammed in a partially open or partially closed position. It is also possible, in the event of mechanical malfunction of the valve module, that the valve member might become jammed or stuck or otherwise fail to respond to control commands. Because of the inaccessibility of the valve module, the operator cannot tell what position the valve is in. Thus, for example, if it is noticed that a hopper load is not emptying properly, it could be because the valve member is stuck shut, or alternatively, it could be that the valve member is open, but that the dredged material is clogged or jammed at the hopper outlet because of the nature of the material. It is most useful for the operator to know the exact position of the valve member in the event of a problem, and this information is not available with prior modules.
Various types of position detecting and indicating systems are known in the prior art. For example, float-type tank level indicating systems are sold by Gems Sensors Division of Delaval Turbine, Inc. But such prior art position indicating systems are not suitable for use in the harsh environment in the bottom of a dredge hopper. The dredged material is typically very heavy and may include large solid objects as described above, and there is considerable turbulence in the vicinity of the hopper valve, particularly during the emptying of the hopper, which subjects the parts of the valve module to considerable buffering and stress.